Organic light emitting diodes (OLEDs) are promising for display applications due to their high power-conversion efficiency and low processing costs. Such displays are especially promising for battery-powered, portable electronic devices, including cell-phones, personal digital assistants, handheld personal computers, and DVD players. These applications call for displays with high information content, full color, and fast video rate response time in addition to low power consumption.
Current research in the production of full-color OLEDs is directed toward the development of cost effective, high throughput processes for producing color pixels. For the manufacture of monochromatic displays, spin-coating processes have been widely adopted (see, e.g., David Braun and Alan J. Heeger, Appl. Phys. Letters 58, 1982 (1991)). However, manufacture of full-color displays requires certain modifications to procedures used in manufacture of monochromatic displays. For example, to make a display with full-color images, each display pixel is divided into three subpixels, each emitting one of the three primary display colors, red, green, and blue. This division of full-color pixels into three subpixels has resulted in a need to modify current processes for depositing different organic polymeric materials onto a single substrate during the manufacture of OLED displays.
One such process for depositing polymer layers on a substrate is ink-jetting (see, e.g., U.S. Patent Application Publication No. 2001/0001050). In order to form an emitting layer with a uniform thickness, proper formulation of the ink and proper design and treatment of the substrate is generally required. However, it has proven quite challenging to properly design and treat substrates to form full-color displays while maintaining suitable device performance (such as efficiency and lifetime). For example, structures used for retaining polymer inks in the subpixels tend to reduce the aperture ratio of a display. In addition, methods used for surface treatment of subpixellated substrates prior to addition of polymer inks can damage the underlying active matrix substrate. Accordingly, there is a need for alternative methods for the cost effective production of full-color EL devices that do not deleteriously effect device performance.